No. A flexing floor or ceiling does great harm to the bass
by causing a dip as well as a resonant smear AND conducts
with hardly any attenuation. A rigid room boundary is generally
preferable unless we are speaking about a wooded structure
with a "non resonant" or "multiresonant" looseness.

I once lived in an all-concrete apartment house. I've never gotten such low bass
from my system.